Apparatuses for projection of image information are used, for example, for the projection of images in virtual reality system. In these systems, the viewer wears a helmet in which a screen is disposed immediately in front of his or her eyes. Images are projected onto the screens via light wave conductors. The ends of the light wave conductors associated with the screens are disposed in the form of light spots arranged evenly in grid fashion on the surface of the screen. The totality of light spots produces a complete image, comparable with LCD screens, etc. Apart from their use in virtual reality systems, the aforementioned apparatuses are also used as monitors in conjunction with a computer or TV receiver, for example. The above mentioned applications all share the feature that it is often desirable to obtain information concerning the viewer, for example his or her eye movements or approach to the screen. This applies more particularly if such apparatuses are used for the diagnosis or therapy of people having faulty vision.
It is known in practice, for example, when the aforementioned apparatus is used in the field of medicine and therapy, to determine eye movements by means of an infrared CCD camera. The camera is connected to an evaluating device which determines the position of the axis of vision of the eye in question from the image supplied by the camera. Such cameras and evaluating devices have proved their value in practice, but their disadvantages are their size and weight and the fact that they must often be placed outside the center of the field of vision. These disadvantages are particularly noticeable if the camera is mounted with the screens in a helmet worn by a person. Moreover, in many cases a light source is required, which illuminates the observed eye. The viewer frequently finds that this additional light source disturbs his or her viewing of the screens. Finally, the miniaturization of such systems is impeded due to the large number of constructional elements required by the prior art systems.